As well known, a glass bulb employed in a cathode ray tube for use in color television sets, computer monitors, or the like basically includes three parts, namely a panel for displaying images, a conic funnel joined to a rear portion of the panel and a cylindrical neck joined to an apex portion of the conic funnel. The panel, the funnel and the neck are made of glass, and particularly the panel and the funnel are formed by press-forming a charge of molten glass called a glass gob into predetermined sizes and shapes. After press-formed, the panel is subjected to a pin sealing process for sealing stud pins, an annealing process performed in an annealing lehr for removing residual stress from the panel by heat-treatment, a lapping process and an inspection process in order, so that a finished panel product is obtained.
Referring to FIG. 1, there is shown a configuration of a glass bulb 10 for use in a cathode ray tube. A panel 20 of the glass bulb 10 includes a faceplate portion 21 for displaying images, a skirt portion 23 extending backward from the perimeter of the faceplate portion 21 and having a seal edge 22 on its back end, and a blend round portion 24 for joining the skirt portion 23 to the faceplate portion 21. The inner surface of the faceplate portion 21 is coated with a fluorescent material for forming images thereon. The blend round portion 24 is also called as a fillet referring to a smoothly curved corner portion connecting the contours of faceplate portion 21 and the skirt portion 23.
A funnel 30 has a body portion 32, which is provided with a seal edge 31 connected to the seal edge 22 of the panel 20, and a yoke portion 33 extending backward from the body portion 32. Further, a neck 40 is connected to the yoke portion 33 of the funnel 30.
Recently, an increasing number of active researches are in progress to reduce the thickness and the weight of the panel, to thereby cut costs in manufacturing the panel for use in the cathode ray tube.
Conventionally, in order to reduce the weight of the panel, the faceplate portion has been designed to have a reduced thickness or the skirt portion has been configured to have a reduced height. However, there has been reported no method for changing the shape of the blend round portion for the purpose of realizing the weight reduction of the panel.